Cracking of a hydrocarbon oil with a silica-alumina-tungsten phosphate catalyst composite



Alfred E. Hirschler, Springfield, and Edward J. Janoski,

Philadelphia, Pa., assignors to Sun Oil Company, Philadelphia, Pa., acorporation of New Jersey Application December 29, 1954 Serial No.478,510

1 Claim. (Cl. 208-114) No Drawing.

This invention relates to a catalytic composition effective in catalyticprocesses for converting hydrocarbons. More particularly, this inventionrelates to new and improved catalytic compositions, their preparation,and to a process for convertinghydrocarbons employing the new catalystwherein a specific hydrocarbon fraction, boiling above the gasolinerange, is converted to gasoline of high octane rating.

The conversion of various petroleum hydrocarbon fractions by processessuch as cracking, reforming, hydroforming, and the like, using a varietyof catalysts and reaction conditions, has been described. Suchheretofore described processes, however, are not suitable for convertingthe hydrocarbon fraction boiling substantially within the range of fromabout 375 F. to 500 F. to high octane gasoline in a single stage.Instead of achieving a good yield of high octane gasoline, there isproduced gasoline hydrocarbons of relatively low octane rating usuallyin low yields, the production of normally gaseous hydrocarbons, such aspropane and butanes, is excessive, and the reduction of catalystactivity is rapid. It has heretofore been necessary to employ at leasttwo stages to convert a petroleum hydrocarbon fraction boiling above thegasoline range, especially a fraction boiling within the range of fromabout 375 F. to 500 F., to high octane gasoline. Such processes usuallyinvolve a cracking stage wherein a portion of the hydrocarbons areconverted to hydrocarbons boiling in the gasoline range, and areforming, or hydroforming, stage to upgrade the octane rating of thegasoline. In the upgrading stage, the use of 'two catalysts in separatereactors with a hydrocarbon separation step between the reactors, or theuse of two catalysts in a single reactor, has heretofore commonly beenrequired.

An object of this invention is to provide a new and improved catalyticcompositioneffective for converting hydrocarbons.

'Another object is to provide a process for converting a hydrocarbonfraction boiling within the range of from about 375 F. to 500 F. to highoctane gasoline in a single stage and in good yield.

A still further object is to provide a process for the preparation of anew and improved catalyst.

Other objects and their achievement, in accordance with the invention,will be apparent from the following.

specification.

' General A new catalytic composition has been discovered which givesimproved results in converting hydrocarbons. The new catalyticcomposition-contains tungsten phosphate, silica and alumina in definedquantities, as hereinafter. discussed. It has been found that this newcatalytic composition is especially effective in converting relativelyhigh boiling petroleum fractions, e. g.,'a fraction boiling withintherange of from about 375 F. to

500 F., to gasoline hydrocarbons of high octane number,

that the formation of normally gaseous hydrocarbons is nited StatesPatent ice '2 substantially reduced as compared to heretofore describedprocesses, and that the normally gaseous hydrocarbons produced have aremarkably high olefinic content so that they are especially valuable inprocesses such as alkylation and polymerization.

The reactions involved in the process of the invention are primarily thecracking of the relatively high molecular weight hydrocarbons tohydrocarbons boiling in the gasoline range, and the dehydrogenation ofhydrocarbons to produce hydrocarbons of higher octane number, such asthe dehydrogenation of naphthenes to produce aromatic hydrocarbons.Hence, the process of the present invention is conveniently designatedherein as dehydrocracking. Other reactions, however,- are involved andassist in producing the high octane hydrocarbons prepared by theprocess, such as the. isomerization of paraffins to produce more highlybranched chain parafiins of rela- .tively high octane number, andcyclization followed by T catalyst As above stated, the catalyticcomposition of the present invention contains tungsten phosphate,alumina and silica. It is important that the weight percent, based onthe final composition, of each component be within the following ranges:tungsten phosphate=0.5 to 10%, alumina=6 to 20% and silica=70 to 94%.The values herein reported for tungsten phosphate have been calculatedfor the complex P O -24WO but it is realized that the material socalculated probably exists in the present catalytic composition as amixture of the designated complex with other complexes between oxides oftungsten and oxides of phosphorus, and that an oxide or oxides oftungsten, as such, may be present in minor quantities. As used herein,tungsten phosphate is used for convenience in designating suchcompounds, complexes, and mixtures thereof, and includes materialsconsisting essentially of tungsten, phosphorus and oxygen.

When the quantity of tungsten phosphate in the catalytic composition isbelow 0.5% by weight, a decrease in the olefinic content of the normallygaseous hydrocarbons is observed, whereas in quantities above 6% byweight, excessive coke formation on the catalyst and excessive.formation. of normally gaseous hydrocarbons are observed. If thequantities of alumina or silica are varied from'the stated ranges, theconversion of the high 'catalyticcomposition' be within the statedranges.

Preparation of catalyst,

Although the catalyticiccmposition of the present invention may beprepared by various means, it is preferred to first prepare a syntheticsilica-alumina composition,

and to depositqthe tungsten phosphate thereon. -Synthetic"silica-alumina compositions are 'well kno'wnascracking-catalysts, and heretofore described methods for theirpreparation'may be employed in preparing the silica alumina portion ofthe present catalyst. For example,

the silica-alumina portion of the catalyst may bejp repared byimpregnating silica with aluminum saltsf 'by directly combiningprecipitated hydrated alumina' 'aiidi-f silica, or by jointprecipitationof' alumina and silicafrorn' aqueous solutions of theirsalts, and by washing, drying, and heating the resulting composition.The resulting silica-alumina composition should have an activity indexof at least 30, and preferably from 40 to 50. Activity index, as usedherein, is a measure of the efficiency of a catalyst for crackinghydrocarbons and is determined by a method described by Alexander,Proceedings Am. Pet. Inst. 27 (III), 51 (November 1947).

Tungsten phosphate is advantageously incorporated with thesilica-alumina composition by impregnating the silica-alumina with anaqueous solution containing a water soluble compound of tungsten and aphosphate. It is preferred to use acids of tungsten and of phosphorus,tungstic acid and orthophosphoric acid being preferred. The impregnatingliquid is advantageously made by preparing a mixture of tungstic acid,orthophosphoric acid and water, and heating the mixture, if necessary,to obtain a solution. The solution is then neutralized, preferably withaqueous ammonium hydroxide, and again heated, if necessary, to obtain asolution. On cooling, any insoluble material is removed such as byfiltering or centrifuging. An additional quantity of orthophosphoricacid is added to the solution to give a final concentration of thephosphate, as desired, within the hereindefined limits.

After impregnation, any excess liquid is removed and the impregnatedsilica-alumina composition dried by heating to from about 80 C. to 200C. for from about 1 to 20 hours and calcined by heating to from about500 C. to 750 C. for from about minutes to 4 hours in contact with anoxidizing gas such as air. Free acids of phosphorus should not bepresent in the final composition, and if necessary, the calcinedcomposition should be washed to insure their absence.

The foregoing procedure, as has been found, yields a catalyst ofexceptionally high activity in producing gasoline hydrocarbons at a highoctane rating from higher boiling hydrocarbons.

Dehydrocracking The reactions involved in the present process forconverting relatively high boiling petroleum hydrocarbons to gasolinehydrocarbons of high octane rating are primarily dehydrogenation andcracking, and hence the overall process is conveniently designated asdehydrocracking. The gasoline product preferably contains onlyhydrocarbons having a molecular weight lower than the hydrocarbons ofthe charge stock, and hence includes only the hydrocarbons which havebeen cracked in the process.

As above stated, the new catalytic composition of the invention isespecially suitable for dehydrocracking hydrocarbon fractions boiling inthe range of from 375 F.

to 500 F. to gasoline hydrocarbons of high octane rating, heretoforedescribedprocesses and catalysts being unsuitable for this conversion.Accordingly, the use of the present catalyst will be described in termsof this.

coke formation. The pressure is preferably maintained at aboutatmospheric pressure, but superatmospheric pressure up to about 100 p.s. i. g. can be used if desired;

'The space velocity must be maintainedwithin the range of from about 0.5to 3. It is preferred to employ a space velocity of from 0.8 to 1.5since within this range there is obtained a high gasoline yield of highoctane number. By space velocity, as used herein, is meant the liquidhourly space Velocity, which is the liquid volume of by drocarbonscharged per volume of catalyst per hour,

In carrying out the process of the invention, it is preferred to passthe hydrocarbon charge through a bed of catalyst under the aboveconditions. By such operation the activity of the catalyst is graduallydecreased, principally due to the deposition of carbonaceous materialsthereon. Periodic regeneration of the catalyst, such as by discontinuingthe operation, flushing the catalyst bed with an inert gas such assteam, flue gas, nitrogen, or the like, and burning off the carbonaceousmaterials by passing an oxygen containing gas, such as air, through thehot catalyst bed, is advantageously employed. Regeneration is generallyadvantageously employed at intervals of from about 10 minutes to 2hours, depending upon the particular operation and reaction variablesbeing used.

Hydrogen preferably is not employed in the process, but a small partialpressure thereof is not deleterious. In some other uses of the presentcatalyst, however, an atmosphere of hydrogen is advantageous, especiallywhere operation is at superatmospheric pressure, as hereinafterdescribed.

Example In order to illustrate a preferred catalytic composition of theinvention and its use in dehydrocracking, a catalytic composition, inaccordance with the invention, was prepared as follows, in which partsrefers to parts by weight:

397 parts of a synthetic silica-alumina cracking catalyst prepared bycoprecipitation, and containing about 13% by weight alumina and about19% water, and having an activity index of about 46, was impregnatedwith an aqueous solution prepared as follows: a mixture of 436 partswater, 21 parts tungstic acid and 1.8 parts of orthophosphoric acid washeated to the boiling temperature of the liquid and then cooled andneutralized with 28% aqueous ammonium hydroxide. The neutralized liquidwas heated to its boiling temperature, cooled, and insoluble materialfiltered. About 23.8 parts of 85% orthophosphoric acid was added. Theresulting solution was used to impregnate the solid silica-aluminacomposition, after which the impregnated silica-alumina was dried byheating to about C. for about 16 hours and calcined by heating to about650 C. for about 2 hours in contact with air.

The resulting composition constitutes a preferred catalytic compositionprepared in accordance with the invention and contained in percent byweight, 4% tungsten phosphate, 12.5% alumina and 83.5% silica. it isimportant that free acids of phosphorus be absent from the finalcomposition.

In order to illustrate the etficacy of this new catalytic compositionfor converting hydrocarbon fractions boiling in the range of from 375 F.to 500 F. to high octane gasoline hydrocarbons, a straight-run petroleumhydrocarbon fraction boiling in the range of fromabout 375 F. to 460 F.,having an aromatic content of about 13% by volume and a naphthenecontent of about 50% by volume was contacted therewith. The followingconditions were employed during the contacting: temperature ofcatalyst=5l2 C., space velocity=l.06, pressure=atmospheric. The catalystbed was regenerated after operation for 20 minutes by burningcarbonaceous materials therefrom with a stream of air as abovedescribed. Products were collected over 10 cycles of operation andregeneration.

A yield of gasoline hydrocarbons, i. e., hydrocarbons from pentane tothose boiling at 350 F., of 26.2% by volume was obtained. There werealso obtained 15.2% by volume of hydrocarbons having 4 carbon atomswhich contained 40.2% by weight olefins, principally isobutylone. Thebottoms fraction, i. e., hydrocarbons boiling over 350 F., constituted54.6% by volume of the charge. Where desired, a gasoline fraction havinga higher end point can be separated from the reaction mixture therebyincreasing the observed yield of gasoline.

However, it is of the gasoline charge stock.

The gasoline fraction had an octane number of 96.9 (ASTM Method D90853)and an aromatic content of 50% by volume.

If the above example is repeated, using as the catalyst thesilica-alumina composition on which was deposited tungsten phosphate inthe above example, the quantity of hydrocarbons having 4 carbon atomsproduced substantially above 20% by volume, and the olefinicconpreferred to maintain the boiling range product below the boilingrange of the tent thereof is only about 30% by weight.

The foregoing example illustrates a preferred embodiment of theinvention, including a preferred catalytic composition and its preferreduse in hydrocracking a refractory, relatively high boiling hydrocarbonfraction to gasoline having a remarkably high octane number. Thecatalyst is also efiective to dehydrocrack other relatively high boilingfractions, such as gas oils boiling from about 400 F. to 750 F. orhigher, to gasoline.

When other catalytic compositions within the scope of the presentinvention are employed, substantially equivalent results are obtained,and when other operating conditions are employed within the rangesherein described, substantially equivalent results are obtained. Theprocess may also be operated batchwise or as a moving bed or fluidizedprocess by maintaining the reaction conditions equivalent to thoseherein described.

The catalyst of the invention can be used in other reactions involvingthe conversion of hydrocarbons, such as destructive hydrogenation usingelevated pressures in an atmosphere of hydrogen, reforming, and thelike, in which catalytic conversion conditions known to be effective insuch processes give good results.

The invention claimed is:

Process of cracking which comprises contacting a straight run petroleumfraction boiling in the range of from 375 F. to 500 F. with a catalystconsisting essentially of, in percent by weight, 70 to 94% silica, 6 to20% alumina and 0.5 to 6% tungsten phosphate and essentially free offree acids of phosphorus at a temperature within the range of from 450C. to 540 C., a space velocity of from 0.5 to 3 and a pressure of aboutatmospheric, and recovering gasoline of high octane rating from thereaction mixture.

References Cited in the file of this patent UNITED STATES PATENTS2,336,600 Fawcett Dec. 14, 1943 2,378,209 Fuller et al. June 12, 19452,463,508 Bates Mar. 8, 1949 2,470,190 Schmerling May 17, 1949 2,496,621Deery n. Feb. 7, 1950 2,500,197 Michael et al. Mar. 14, 1950 OTHERREFERENCES Ser. No. 390,534, Pier et al. (A. P. C.), published May 18,1943.

